EXERCISES FOR WEEK 10
week10-1

The program movelight.cpp rotates a light source around an object. When the left mouse button is pressed, the light position rotates an additional 30 degrees. A small, unlit, wireframe cube is drawn to represent tthe position of the light in the scene.

Make the light translate past the object (move left - right or up - down) instead of rotating around it. Hint: Use glTranslated() rather than the first glRotated() in display(), and choose an appropriate value to use instead of spin.

 
week10-2 Continuing with the program movelight.cpp, try to create a light that moves along with the viewpoint. You need to set the light position before the viewing transformation. Then the viewing transformation affects both the light and the viewpoint in the same way. In the following code, the light position is defined in init(), which stores the light position at (0,0,0) in eye coordinates. In other words, the light is shining from the lens of the camera.

GLfloat light_position() = {0.0, 0.0, 0.0, 1.0};
glViewport(0, 0, (GLint) w, (GLint) h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(40.0, (GLfloat) w/(GLfloat) h, 1.0, 100.0); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glLightfv(GL_LIGHT0, GL_POSITION, light_position);

If the viewpoint is now moved, the light will move along with it, maintaining (0,0,0) distance, relative to the eye. Next, the global variables (ex,ey,ez) and (upx,upy,upz) control the position of the viewpoint and up vector. The display() routine that's called from the event loop to redraw the scene might be this:

static GLdouble ex,ey,ez,upx,upy,upz;
void display(void)
{
    glClear(GL_COLOR|GL_DEPTH);     
    glPushMatrix();
      gluLookAt (ex,ey,ez,0.0, 0.0, 0.0, upx, upy, upz);
      glutSolidTorus (0.275, 0.85, 8, 15);
    glPopMatrix();
    glFlush();
}

when the lit torus is redrawn, both the light position and the viewpoint are moved to the same location. As the values passed to gluLookAt() change and the eye moves, the object will never appear dark, because it is always being illuminated from the eye position. This method of moving the light can be very useful for simulating carrying a candle or lantern. The light position specified by the call to        glLightfv(GL_LIGHTi, GL_POSITION, position)
would be the x,y, and z distance from the eye position to the illumination source.
week10-3 Go through the recursive subdivide algorithm (by hand) and determine the vertices generated if the original vertices are: v1 = (0,0); v2 = (4,4); v3 = (8,0) and the depth is 2. Sketch the resulting figure.

week10-4 Write a function subdivide( ) that takes four input parameters: 3 vertices (double) and a depth (int) and draws the resulting subdivided triangle. Test it out with various levels.
week10-5

Copy the spotlight demo program in

/classes/cs3014/files/Lighting/spotdemowall.cpp


to your directory. Compile and execute it to make sure you understand what it is doing. Be sure to try all the options.